1、导入所需包及训练、测试的数据

import tensorflow as tf
import numpy as np
import matplotlib.pyplot as plt
from tensorflow.examples.tutorials.mnist import input_data
mnist = input_data.read_data_sets('datasets', one_hot=True)

备注：自动下载所需数据到指定的文件夹，文件夹名称datasets

2、原始数据处理

trainimg = mnist.train.images
trainlabel = mnist.train.labels
testimg = mnist.test.images
testlabel = mnist.test.labels

2-1、查看数据的形状

print(trainimg.shape)
print(trainlabel.shape)
print(testimg.shape)
print(testlabel.shape)

output:
(55000, 784)
(55000, 10)
(10000, 784)
(10000, 10)

2-2、显示图片

i = 5
curr_img = np.reshape(trainimg[i,:], (28, 28))
plt.imshow(curr_img, cmap=plt.get_cmap('gray'))
plt.show()

output:

备注：
np.reshape() : 为数组提供新形状而不更改其数据
trainimg[i,:] : 提取数组第i行的全部数据

3、创建输入数据的特征向量

x = tf.placeholder(tf.float32,[None,784])
y = tf.placeholder(tf.float32,[None,10])

4、创建模型参数

W = tf.Variable(tf.zeros([784,10]))
b = tf.Variable(tf.zeros([10]))

5、正向传播，计算输出值

actv = tf.nn.softmax(tf.matmul(x,W) + b)

6、计算损失函数

cost = tf.reduce_mean(-tf.reduce_sum(y*tf.log(tf.clip_by_value(actv,1e-10,1.0)) reduction_indices=1))

7、使用梯度下降法进行优化

learning_rate = 0.01
optm = tf.train.GradientDescentOptimizer(learning_rate).minimize(cost)

8、判断正确结果与预测结果是否一致

pred = tf.equal(tf.argmax(actv, 1), tf.argmax(y, 1))

备注：
tf.argmax(input, dimension, name = None):返回最大数值的下标
dimension = 0: 按列找 ; dimension = 1 :按行找

9、计算正确率

accr = tf.reduce_mean(tf.cast(pred, tf.float32))

10、初始化模型参数

init_op = tf.global_variables_initializer()

11、定义常量

training_epochs = 100    #训练的轮数
display_step = 5        #用来比较、输出结果

12、使用batch梯度下降法进行训练

with tf.Session() as sess:
    sess.run(init_op)
    costs = []
    #对于每一轮的训练
    for epoch in range(training_epochs):
        avg_cost = 0.
        
        sess.run(optm, feed_dict={x: trainimg, y: trainlabel})
        feeds = {x: trainimg, y: trainlabel}
        avg_cost += sess.run(cost, feed_dict=feeds) / training_epochs
        
        if epoch % display_step == 0:
            feed_train = {x: trainimg, y: trainlabel}  
            feed_test = {x: testimg, y: testlabel}
            
            train_acc = sess.run(accr, feed_dict=feed_train)
            test_acc = sess.run(accr, feed_dict=feed_test)
            
            print("Eppoch: %03d/%03d cost: %.9f train_acc: %.3f test_acc: %.3f" %
                  (epoch, training_epochs, avg_cost, train_acc, test_acc))
            
        costs.append(avg_cost)
            
print("Done.")

# plot the loss
plt.plot(costs)
plt.ylabel('cost')
plt.xlabel('iterations ')
plt.title("Learning rate =" + str(learning_rate))
plt.show()